1. Field of the Invention
The present invention relates to a printed circuit board on which a four-way lead flat package IC is mounted by soldering using a jet-flow type soldering bath.
2. Description of the Related Arts
In general, due to increasing demands on printed circuit boards for increasing component mounting density, a need has been arising in mounting a four-way lead flat package IC with a narrowed pitch. On the other hand, practical application of lead-free solder, reflecting environmental concerns, has been progressing rapidly. However, lead-free solder has poor soldering reliability than that of lead-containing eutectic solder that has been used in the related art practice. Therefore, short-circuiting has been encountered due to soldering bridges between leads of the four-way lead flat packages IC and the like.
In the related art, in order to prevent the occurrence of the soldering bridges, attempt has heretofore been taken to provide a printed circuit board of this kind prepared with side solder drawing lands, formed in a right-angled isosceles triangle shape, and a rear solder drawing land formed in a quadrate shape (see, for instance, Patent Document 1).
Further, another attempt has been taken to provide first and second soldering lands in separate areas to form side or rear solder drawing lands (see, for instance, Patent Document 2).
Furthermore, another attempt has been taken to provide an eyelet on one side of an area between front soldering land groups and rear soldering land groups while forming a lattice-shaped solder drawing land on the other side of the area between the front soldering land groups and the rear soldering land groups and in a trailing area of the rear soldering land groups (see, for instance, Patent Document 3).
[Patent Document 1] U.S. Pat. No. 2,635,323 (on page 3 and FIG. 1)
[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-329955 (on pages 4 to 5 and FIGS. 1 to 5)
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-175186 (on pages 7 to 8 and FIGS. 8 to 11)